Physicists Hunt Weird Antimatter Beneath Earth

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Scientists have tentatively identified several particles lurking
deep inside the Earth's mantle that could reveal how much heat
the planet produces and confirm that the Earth formed from
materials from the sun.

The wacky particles are called geoneutrinos, or the antimatter
partners of neutrinos (exotic fundamental particles that can pass
right through Earth), that form deep within the Earth's mantle.
Every matter particle has an
antimatter partner particle that has an opposite charge, and
when the two meet they annihilate each other. The findings were
detailed described March 11 in the preprint journal
arXiv.org.

Geoneutrinos aren't the only particles scientists are hoping to
find inside Earth. An experiment using the Earth as a
source of electrons recently narrowed down the search for
a new force-bearing particle, possibly the so-called
unparticle, placing tighter limits on the force it carries.

Giant Engine

When Earth formed, the radioactive
elements thorium and uranium were distributed in Earth's
interior at different concentrations within the crust (the
planet's outer layer) and mantle. As these elements within the
mantle radioactively decay, they give off heat and also form
subatomic particles known as geoneutrinos, said study co-author
Aldo Ianni, a physicist at the Gran Sasso National Laboratory in
Italy.

The heat formed from this decay is the engine that drives the
motion of the viscous, oozing material that forms the Earth's
mantle. That, in turn can shift the tectonic
plates, causing
earthquakes. Whereas researchers have models to predict how
much heat is generated inside the Earth, measuring it has proved
tricky. [ 50
Amazing Facts About Planet Earth ]

That's partly because mantle lies miles beneath the Earth's
surface, so "if you want to understand how much heat is produced
by these radioactive elements, the only way today to understand
how much is this so-called radiogenic heat is through the
geoneutrinos," Ianni said.

To do so, researchers at the Gran Sasso underground laboratory,
which is nearly a mile below a mountain in Italy, looked for
signals in a vast pool of oil-based liquid that scintillates, or
produces flashes of light when particles such as protons pass
through it. When geoneutrinos pass through the scintillating
liquid they bump into protons and emit a positron and then a
neutron, creating a distinctive signal, Ianni told LiveScience.

Many of the particles they initially identified actually came
from nuclear reactors from power plants. But by measuring the
energy levels of the neutrinos, they could isolate the 30 percent
that came from the
Earth's mantle, Ianni said.

The geoneutrinos are created from the decay of radioactive
thorium and uranium in a reaction that gives off a known amount
of heat. As a result, how frequently the researchers find the
particles can reveal the quantity of the radioactive elements
lurking in Earth's mantle, and in turn how much heat they
generate. That can help scientists refine their knowledge of
plate tectonics, Ianni said.

But it may also confirm the theory that the Earth formed from the
sun, Ianni said. Meteorites that come from the solar system's
early history contain distinctive ratios of uranium and thorium
that very closely mirror the composition of the sun's surface. By
comparing that ratio with the amount found inside the Earth, they
can confirm the Earth's solar origins.